Electric discharge apparatus



March 12, 1957 H. w. VAN NESS ETAL 2,785,284

ELECTRIC DISCHARGE APPARATUS 3 Sheets-Sheet 1 Filed July 29, 1953 ALA/L'- ALZ INVENTORS WITNESSES; SEQUENCE TIMER %*%A v $6M G n,

Hubert W. VonNess 8 Edward C. Hurtwig.

Fig. IA.

ATTORNEY March 12, 1957 w. VAN N555 ET AL 2,785,284

ELECTRIC DISCHARGE APPARATUS Filed July 29, 1955 3 SheetsSheet 2 Flg. 2. L3

LI L2 Vol'toge HTZO N22 FSV;

FORGE CONTROL UNlT ITNESSES: INVENTORS Hubert W. Van Ness 8 ggword c. Hortwig.

March 1957 H. w. VAN NESS ETAL 2,785,284

ELECTRIC DISCHARGE APPARATUS Filed July 29, 1953 3 Sheets-Sheet 3 REVERSING UNlT L m T N O 0 UNIT INVENTORS WITNESSES Hubert W. Van Ness 8 w M Seward c. Horfwig. J 9 7 A, x W ATTORNEY United States Patent O ELECTRIC DISCHARGE APPARATUS Hubert W. Van Ness, East Aurora, N. Y., and Edward C. Hartwig, Walnut Creek, Califl, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 29, 1953, Serial No. 370,997

9 Claims. (Cl. 219-108) Our invention relates to electric discharge apparatus and has particular relation to such apparatus for controlling Welding systems.

In recent years, the welding art has been extended to the welding of aluminum and its alloys and like metals, such as magnesium and its alloys. These materials are to a large extent used in air frames and similar structures, and particularly for the former, it is essential that the welds be uniformly sound. It has been found that to assure soundness of the welds, each weld must be subjected to a forging operation. The forging is effected by increasing the pressure applied between the electrodes and the material being welded at a predetermined instant after the welding current is initiated and preferably while it is still flowing, above that applied during the squeeze interval before the welding current flows. The instant in the weld interval when the additional or forge pressure is applied is critically governed by the composition and properties of the material being welded and the conditions under which the welding takes place, for example, when a current is initiated, or on the magnitude of the welding current. High precision in the timing of the application of the forge pressure is therefore essential.

It has been the practice to apply the forge pressure by opening a valve between a source of fluid pressure and the cylinder within which the piston that applies the pressure moves. In accordance with the teachings or the prior art of which we are aware, the precision demanded in the forging operation may at least to a limited extent be achieved by controlling this valve from a solenoid which is actuable by direct current. To achieve any reasonable accuracy and reliability with apparatus including a direct current solenoid, it is essential that the solenoid valve be capable of responding in a very short time interval to the current supplied to the solenoid, and it has been found that the required fast-action, direct-current solenoid valve and its associated equipment is highly costly.

it is accordingly broadly an object of our invention to provide welding aparatus including highly accurate and highly reliable means for applying forge pressure to the work or material being welded.

Another object of our invention is to provide low-cost facilities for use in welding apparatus for applying forge pressure to the work with the accuracy and reliability demanded in the making of uniformly sound welds.

An incidental object of our invention is to provide welding apparatus including facilities for applying forge pressure in the operation of which it shall be possible to aply the forge pressure at any time during the interval during which current fiows.

Anoher specific object of our invention is to provide welding apparatus including means for applying forge pressure when the welding current is first initiated or at any time during the interval during which the welding current flows.

An incidental object of our invention is to provide a novel electronic circuit which is particularly suitable for achieving the above stated objects and in addition has other uses.

A further incidental object of our invention is to provide a novel solenoid control circuit which is particularly suitable for achieving the above stated objects and in addition has other uses.

A further incidental object of our invention is to provide welding apparatus which is adapted to be energized from a polyphase source and which includes highly precise but low-cost facilities for applying forge pressure.

In accordance with our invention, we provide welding apparatus in which the forge pressure is applied by actuation of an ordinary alternating :current solenoid valve rather than the high cost, fast-action, direct current solenoid valve. The solenoid of the alternating current valve is supplied from a forge control unit con trolled by a timer circuit which permits current to be conducted through the solenoid during a selected time interval. The circuit also includes means for determining the phase angle in the half periods of the alternating current at which the supply of current to the solenoid is initiated after the timer circuit times out. This means in efiect constitutes a Vernier adjustment for the initiation of the forge pressure.

The timing of the timer circuit is controlled from a sequence timer of the usual structure including means, usually a weld timer circuit including a thyratron, for initiating and timing flow of welding current. Such a sequence timer also includes means for initiating the timing of the weld time circuit, and the latter means is actuated a predetermined time interval before the weld time circuit. In accordance with our invention, the timing of the operation of the forge control unit is initiated by the means which initiates the timing of the weld time circuit. Thus, the timing of the forge control unit is initiated before the weld timing circuit acts to start the welding current, and the forge pressure may be applied at any time during the welding interval from the instant when the welding current starts to flow to the instant when the welding current stops, or even after this instant.

The novel features that we consider characteristic of our invention are discussed generally above. The invention itself, both as to its organization and its method of operation, together with additional objects and advantages thereof, will be understood from the following description of a specific embodiment when read in connection with the acompanying drawings, in which:

Figs. 1A, 1B and 10 together constitute a circuit diagram of a preferred embodiment of our invention; and

Fig. 2 is a graph illustrating an important feature of our invention.

Description While our invention is applicable to welders of all types, those adapted to be supplied from single-phase supplies, as well as those adapted to be supplied from polyphase supplies, it is shown herein as incorporated in a welding system of the polyphase low frequency type, such as is disclosed in an application Serial No. 272,818. filed February 21, 1952, to Clarence B. Stadum, Hubert W. Van Ness and Edward C. Hartwig, which we will call hereinafter the Stadum application. The parts of the apparatus disclosed in the Stadum application, which do not concern our invention, are not shown in detail herein, and reefrence is made to the Stadum application for the detailed description of these parts. So that the relationship to the Stadum aplication may be clear, the labelling is to the extent practicable, the same as in the Stadum application.

The apparatus shown in the drawings includes a Welder, a Power Supply Unit, a Heat Control Unit, a Post-Heat Unit, a Reversing Unit, a Sequence Timer and a Forge Control Unit. Our invention resides in the Forge Control Unit and in its cooperative relationship with the Welder and the Sequence Timer and only the Forge "Control Unit, the Welder and the Sequence Timer are shown in detail. I g The apparatus disclosed herein derives itspower from the main supply conductors Ll, andlfi of a threephase power Supply. The Sequence Timer and certain of the other components are supplied from auxiliary supply conductors AL and ALZ, which derive their power frond the conductors L2 and L3 through a transformer TQ The Welder includes aweiding transformer W having a primary I and a secondary S; is explained in the Stadum application, the prirnary p is adapted to be connected to, and supplied from, the fowcr' Supply Unit, either through the contacts K1 and K2, or the contacts K3 and K4, depending on the setting of the Reversing Unit.

The welding electrodes El and B2 are connected across the secondary S. The electrode E2 is fixed, and the electrode E1 is movable by a piston which is hydraulically actuable. The fluid for actuating the piston is derived from a fluid supply controlled from initial pressure valve VI and forge pressure valve VF. The initial pressure valve VI is actuable by a solenoid SV adapted to be connected between the conductors L2 and L3 through the contact 19 of a starting relay SR1. The forge valve is'adapted to be actuated by a solenoid SVF which is supplied from the Forge Control Unit. SolenoidsSV and SVF are of the usual low cost alternating current type. a

The Welder also includes a pressure switch PS which is actuated by a piston (not shown) in a cylinder PR which is interposed in the fluid supply system.

The SequenceTirner is of the type disclosed in the Stadurn application and includes a squeeze thyratron ST, a weld 'thyratron WT, a hold thyratron HT and an off thyratron OT and associated networks including a squeeze network SN, a weld network WN, a hold network RN and an off network ON. In addition, the Sequence Tirner includes the auxiliary thyratrons ATZ, AT3, AT4, ATS and ATE, the double diode D2 and'the auxiliary networks AN Z, AN, AN4, and ANS.

The squeeze thyratron ST includes an anode 239, a cathode 2'21 and a control electrode 233%. 219 andthe cathode 221 are connected in a circuit extendingfrom conductor A; through the coil of relay SR1, the conductor 224i,the anode 2 19, the cathode 223., conductor 222, the starting 'switch FS, when it is closed, or the contact 412 of the relay SR1, when it is closed, to the conductor ALL The oft network ON includes a capacitor 225 shunted by a fixed resistor 229 and a variable resistor 227. This network is connected between the control electrode 231 and the cathode 221 'of the thyratron ST through a grid resistor 235.

The weld thyratron includes'an anode 259-, a cathode 260, a first control electrode 359 and a second control electrode 344). The anode 259 and cathode 269 of the weld thyratron WT are connected in a circuit extending from conductor AL2 in the Heat Control Unit through tcertainirnpedances in this Unit which do not concern WT. Another he'tworli A1 15 includes a capacitor 366 and a resistor 368, and it is connected between the other The anode 1 control electrode 340 and the cathode 260 through a grid resistor 372.

The hold thyratron HT includes an anode 376, a cathode 273 and a control electrode 271. The anode 376 and the cathode 273 are connected in a circuit eX- tending from conductor AL; through the network ANS, anode resistor 374, anode 376 cathode 273 to conductor A12. The weld network WN includes a capacitor 265' shunted by a fixed resistor 5 91 and variable resistors 267 and 2:59. This network is connected between the control electrode 271 and the cathode 273 of the hold thyratron HT through a grid resistor 283.

The oft thyratron OT includes an anode 237, acathode 239 and a control electrode 287. The anode 237 and cathode 23% of the, off thyratron are connected in a circuit extending from conductor ALE through the starting switch FS, or the contact 4 12, the conductor 222, the or? network ON, conductorZdl, the anode resistor 242, the anode 23?, the cathode 23$, to the conductor ALZ. The bold network includes a capacitor 283 shunted by the fixed resistor 235 and a variable resistor 23%. This network is connected between the control electrode 257 and the cathode 239 -of the off thyratron OT through a grid resistor 29?. r V

The auxiliary thyratron ATZ includes an ode 317, a cathode 319 and a control electrode 322. e network ANZ includes a capacitor 3 37 shunted by a resistor The network ANZ and the thyratron ATE are connected in a circuit extending from the conductor ALZ through the network ANZ, the anode resistor 315, the anode 31", the cathode 319, the conductor 22 2, the starting switch FS or the contact 412 to the conductor ALE. The cit network ON is connected between the control electrode 321 and the cathode 319 of the thyratron ATZZ through the grid resistor 325 The thyratron AT3 has an anode 355, a cathode 3&5 and a control electrode 311. The squeeze network SN has a capacitor 2 shunted by a fixed resistorZd? and a variable resistor 245. The thyratron ATE and the squeeze network SN are connected in a circuit extending from the conductor ALE through the network SN, the anode resistor 333, the anode 355, the cathode fetid to the conductor ALE. The network ANZ is connected between the control electrode and the cathode 3th? through a grid resistor 313.

The 'thyratron ATd has an anode 343, a cathodefifi-S and a control electrode. 337. The network ANS includes afcapaci'to'r 343 shunted by a resistor lid-Sand the secondary H83 of the heater transformer Hi3 for the cathode 3&5 of thyratron ATE. This thyratron is connectedin several branch circuits. One of these extends from the conductor ALL. in the Post-Heat Unit through the secondary HS7 of the heater transformer HT7, a resistor 4G7, conductor iii, pressure switch PS when it is closed, conductor 5%, the anode resistor 34%), the anode 341, and the cathode 339 to the conductor ALL Another circuit extends from the conductor A142 through atir'ne constant network ANZti-in the Forge Control Unit,

a rectifier 524i, a conductor 523, the pressure switch PS,

the conductor 5%, the resistor 349, the anode Edi and the cathode 339 to the condnctorALll. A third circuit extends from the conductor AL2 through the network AN3, the conductor 52.3, the pressure switch PS, the conductor 5%, the anode resistor 34), the anode 341, the cathode 33? to the conductor ALE. The control electrode 337 of the thyratron A'M is connected to its cathode 339 through grid resistor and the squeeze network SN.

The thyratron ATS has an anode 353, a cathode 347, and a control electrode 351. The doubie diode D2 has a corn-rnon cathode 35d and anodes 362 352. The anode and cathode of the thyra-tron ATE are connected in a circuit extending from the conductor ALE through the network AN i, the diode section 362-354, the anode resistor 356, the anode 353, the cathode 347 to the conductor ALE. The thyratron ATS is also connected in a circuit supplied from the secondary S1 of the transformer T1. This circuit extends from one terminal of the secondary through the section 352-354 of the double diode D2, the current limiting resistor 356, the anode 353, the cathode 347, the weld network WN to the other terminal of the secondary S1. The network AN3 is connected between the control electrode 351 and the cathode 347 through a grid resistor 349.

The thyratron AT6 has an anode 371, a cathode 367, a first control electrode 365 and a second control electrode 428. The anode and cathode of this thyratron are connected in a circuit extending from the conductor AL2 through the hold network HN, the anode resistor 369, the anode 371, the cathode 367 to the conductor AL1. The first control electrode 365 is connected to the cathode 367 through a grid resistor 363 and through the network ANS. The second control electrode 428 is connected to the cathode directly through the repeat contact 503 of the repeat non-repeat switch RNR in the repeat position of the switch. The same control electrode is adapted to be connected through the other contact 505 of the switch RNR and through the grid resistor 430 to the off network ON in the non-repeat position of the switch.

The Forge Control Unit includes a pair of thyratrons 1TSV and 2TSV. Each thyratron has an anode 531, a cathode 535 and a control electrode 535. The anodes of the circuits of the thyratrons are supplied from'the conductors L1, L2 and L3 though a pair of selector switches 18W and 28W. Each of the switches has a movable contact 541 and 561 which are movable together and a plurality of fixed contacts 543, 545, 547, 549, 551, 553 and 563, 565, 567, 569, 571, 573 arranged so that they may be engaged in succession as a movable contact (541 or 561) is moved over its path. The first contact 543 and the last contact 553 of switch 18W are connected to the conductor L1; the second and third contacts 545 and 547 are connected to the conductor L2, and the fourth and fifth contacts 549 and 551 are connected to the conductor L3. The first and second contacts 563 and 565 of the switch 25W are connected to the conductor L3, the third and fourth contacts 567 and 569 are connected to the conductor L1, and the fifth and sixth contacts 571 and 573 are connected to the conductor L2. Thus, as the movable contacts of the switches 1SW and 25W move together over the fixed contacts the following conductors are connected in succession between the terminals of the movable contacts: L1L3, ,L2-L3, L2- L1, L3-L1, L3-L2, L1--L2. v

The conductors L1, L2 and L3 are usually connected each to the three buses of a three-wire, three-phase system. Under such circumstances, the potentials which appear across the movable contacts 541 and 561 of the switches 18W, 28W, as these contacts are set on successive sets of fixed contacts, are displaced in phase by 60. This may be understood by consideration of Fig. 2 in which voltage is plotted vertically and time horizontally. The sine curves of Fig. 2 which are labeled L1, L2 and L3, represent the potentials on the conductors L1, L2 and L3 with reference to an artificial neutral. The potential which appears between the movable contacts 541 and 561 of the switches 18W and ZSW for any setting of these contacts is equal to the difierence between the potentials of the buses to which these contacts are connected. Thus, with the switches set in the first position, the potential between the movable contacts 541 and 561 would be represented by a curve corresponding to the difference between the ordinates of the curves L1 and L3. Such a curve would be a sine wave, and its phase position could be determined by observing where the curve passes through zero, that is where the ordinates of the curves L1 and L3 are equal and opposite; and that is at the point labeled L1-L3. In the second position of the switches, the curves L2 and L3 are to be considered. In this case, the curve representing the actual potential differences passesthrough zero at the point labeled L2L3 which is displaced by 60 from the point labeled L1-L3. Similarly, for the other positions of these switches, the curves representing the poten tials between the movable contacts of the switch pass through zero at the points labeled L2L1, L3,-L1, L3 L2, and L1-L2. It is seen that these points are progressively displaced in phase by 60 or A5 of a period, and thus as the movable contacts 541 and 561 move from one position to the other, the potential derivable at these contacts is advanced by 60.

The anodes 531 and cathodes 533 of the thyratrons 1TSV and 2TSV are connected in antiparallel between the movable contacts 541 and 561 of the switches 15W and ZSW through the solenoid SVP of the forge pressure valve VF. This solenoid being of the alternating current type may be energized by current flowing through the thyratrons 1TSV and ZTSV. The thyratrons 1TSV and ZTSV are controlled from the forge timing circuit. This circuit includes the forge thyratron FT and the auxiliary thyratron AT20, and the network ANZO and the network FN. The forge thyratron FT, has an anode 531, a cathode 583 and a control electrode 585. The thyratron AT20 has an anode 591, a cathode 593, a first control electrode 595 and a second control electrode 597. The network FN includes a capacitor 599 shunted by a fixed resistor 601 and a plurality of variable resistors 603 and 605 which may be set to determine the rate of which the capacitor 599 discharges when it is charged.

The network AN20 includes a capacitor 609 shunted by a resistor 611. The anode-cathode circuit of the thyratron FT is supplied with potential derived from the movable contacts 541 and 561 of the switches 15W and 2817! through the transformer T11. The primary P11 of this transformer is connected across the movable contacts 541 and 561. The secondary S11 of the transformer is connected between the anode 581 and cathode 583 of the thyratron FT through an anode resistor 613, the primary P12 of a control transformer T12, a contact 615 of the starting relay SR1, and 'a switch FSW which is closed to set the apparatus for forge. The network FN is connected between the control electrode and the cathode of the thyratron FT through a grid resistor 617.

The control transformer T12 has two secondaries 1812 and 2812. The first secondary 1812 is connected across a resistor 619; the other secondary 2812 is connected through a rectifier 621 across a network AN21 consisting of a capacitor 623 shunted by a resistor 625. The first resistor 619 is connected between the control electrode 535 and the cathode 533 of the thyratron ZTSV through a bias and a grid resistor 627. The network AN21 is connected between the control electrode 535 and the'cathode 533 of the thyratron 1TSV through a bias and another grid resistor 62?. The bias is in each case adequate to maintain the thyratrons 1TSV and ZTSV, respectively, non-conducting in the quiescent condition of the apparatus. The potential which appears across the secondaries 1812 and 2812 when the primary P12 conducts, is adequate to counteract the bias in each case.

Thyratron FT conducts only during half periods of the potential impressed by the secondary S11. The secondaries 1812 and 2812 are so poled that the potential induced in the secondary 1S12 counteracts the bias in the control circuit of thyratron 2TSV during the half period when the anode of this thyratron is positive relative to the cathode. Thyratron ZTSV then conducts simultaneously with thyratron FT. During this same half period, the left-hand terminal of secondary 2512 is positive relative to the right-hand terminal, and the capacitor 623 of network AN21 is charged so that the control electrode 535 of thyratron 1TSV is positive relative to the cathode 533. But, during this half period, the anode 531 of thyratron 1TSV is negative relative to the cathode 533. During the succeeding half period when the anode of thyratron 1TSV is positive relative to the cathode,

7 ALB, are supplied with potential.

spite of the fact that thyratron FT isduring this half period non conducting. Thus, for each half period during which thyratron FT conducts, thyratrons lTSVand ZTSV conduct a full period.

Thyr'atron ATM is also supplied from the secondary. 31.1 but is connected in opposite phase to the thyratron FT. Thus, the anode-cathode circuit of the thyratron ATZti extends from the upper terminal of secondary SJ through network FN, an anode resistor 631, the anode 591 and cathode 5% of the thyratron ATZU to the lower terminal of secondary Sill. The first-control electrode 595 of thyratron ATZQ is connected to the cathode 593 through a grid resistor 633 and a time-constant network ANZ'Z consisting of a capacitor 635 shunted by a resistor 637 and the secondary HSZiiof the cathodeheater transformer BT25 for the thyratron ATZQ The other control electrode 597 is connected to the cathode 593 the thyratron ATZ-i through a grid resistor 639 and the network ANZiP. The network ANZZ produces a ripple in the control circuit of the thyratron A1 29 so that when this thyratron ATZtl is'conditioned toconduct by the discharge of the network ANZt it begins to conduct at an instant displaced by about of a period from the point of zero potential in the positive half period of the potential supplied by the secondary S11. Thus, in the stand-by condition of the apparatus, false operation of the thyratron AT20 is precluded because network Al lfii charges belore thyratron ATZt) can conduct. The Power supply Unit, the Heat Control Unit, the Reversing Unit and the Post-Heat Unit have the structure described in the Stadurn application. 1

S land-by in the stand-by condition of the apparatus, the power switches or'circuit breakers (not shown) for the apparatus are closed, and the conductors L1, L2, L3, and ALl and Under such circumstances, heating current is supplied to the cathodes of all of the thyratrons, and the latter are in condition to conduct. If the welding is to include a forge operation the switch FSW is closed.

.it may be assumed that the Sequence Timer is set for repeat operation, as shown in the drawing. The sec ond control electrode 423 of the thyratron'AT6 is then connected to its cathode 367., and the contact 597 across the variable resistor 227 isopen.

Thyratrons ST and ATZ are non-conducting because the s. itch PS and the contact are are open. thyratron is non-conducting, relay SR1 is deenergized, contact 19 is open, solenoid SV is deenergized and valve V1 is closed. Because thyratron ATZYis nonconducting network ANZ is discharged, and thyratron ATS is conducting. Network SN is thenrcharged, and thyratron AT is non-conducting. Because thyratron AT4 is nonconducting, several conditions exist in the system. The network ANS is discharged, the Post-Heat Unit is not in operation, and the network ANZQ is discharged,

Because the network AN3 is discharged, the thyratron ATS is conducting, and the network ANd, and the net-, wo k WN are both charged through the double diode D2 which is also conducting. Because the network vAN Z is charged, the weld thyratron WT is non-conducting. The Heat Controi Unit then is not energized and the Power Supply Unit is quiescent. Current then does not flow through the primary P of the welding transformer W.

Because the network WN is charged, thyratron HT is non-conducting. The network ANS is then discharged: and thyratron ATifi is conducting. The network HN is then charged and thyratron OT is non-conducting. The network ON is then uncharged and thyratrons ST and ATE are capable of conducting during the first positive halfperiod immediately following the closing of the switch FS. Q In the Forge Control Unit, the thyratron ATZtP is Because conducting because network ANZ!) is uncharged. Network FN is charged and the thyratron FT is non-conducting The primary P12 then does not conduct urrent, and the thyratrons iTSV and ZTSV are non-conducting so that the solenoid SVF is deenergized and the valve VF isclosed.

Operation In preparing the apparatus for a welding operation the forge network PN is set to yield the desired timing for start of the forge interval, and a Vernier adjustment is made by setting the switches 18W and 128W at the proper fixed contacts. The primary Pit. is then supplied with potential displaced in phase by a fraction of a period corresponding to the settings of the switches 15W and 25W. In the situation shown in the drawings, this displacement lags the potential between the conductors L2 and L3 by 60. The potential between the buses ALl and ALZ is in phase with the potential between the buses L2 and L3, and thus the potential across the primary P11 lags the potential between the buses ALT and ALZ by 60".

To initiate a welding operation, the work M is disposed on electrode E2 and the start switch FS is closed. The thyratrons ST and AT2 are then immediately rendered conducting. The current flow through the thyratron ST energizes the relay SR1 and'its contacts close. At the upper contact 19, the circuit through the solenoid SV is closed. At the contact 412, the coil of the relay S31 is locked in independently of the start switch F5, and at the lower contact, the circuit through the forge thyratron FLT is closed. When the solenoid SV is energized, the valve VI is opened, and pressure is supplied to cause electrode E1 to engage the work M. When the pressure built up between the electrodes E1 and E2 and the work applied to the work and pressure switch PS to close.

M is adequate, the pressure switch PS is closed.

When the thyratron ATZ conducts, it immediately charges the network ANZ impressing a blocking potential on the thyratron AT3.. The thyratron ATS is connected in opposite phase to the thyratron AT2 and conducts during the half periods following those during which the anode-cathode potential of the thyratron ATE is positive. In this case, the thyratron ATE has charged the network AN2 at the beginning of the half period following the conduction of the thyratron ATZ. Thyratron ATE; then fails to conduct during the half period following the con-- dnction of thyratron AT2.

When thyratron AT3 becomes non-conducting, the network SN discharges. This network is set to discharge in artime interval adequate to permit pressure to be At the end of this time interval which is called the squeeze interval, network SN has discharged sufliciently to permit thyratron AT4 to. conduct. The conduction of thyratron ATd has several effects. First, the timing or" the Postl-ieat unit'is started; this does not concern the invention. In addition, the network ANS is charged to COIlii Flt: the timing of the Sequence Timer. Thirdly, the network AN20 is charged. When the network ANZtl is charged, the Lhyratron ATM is rendered non-conducting, and the network FN starts to time out. While the network FN is timing out, the timing of the Sequence Timer continues.

Because the network ANS is charged, thyratron ATS is rendered non-conducting. This thyratron is supplied with potential'in opposite phase to the potential of thyratron AT4 and is for the first time rendered non-conducting during its positive half period of anode-cathode potential immediately following its first negative half period during which thyratron AT4 conducts. This operation is assured because the winding H83 introduces a ripple .in the network ANS which causes the thyratron ATS tobe fired, when it is firedQat an instant delayed by about ,5 of a period from the instant. of zero anodecathode potential. When the thyratron ATd conducts,

- the networkANl': is charged at the beginning of the half period,'and 'thyrat'ron' ATS cannot become conducting;

When thyratron ATS becomes non-conducting, network AN4 discharges, permitting thyratron WT to conduct. Thyratron WT energizes the Heat Control Unit which in turn energizes the Power Supply Unit to supply current to the primary P, as is explained in the Stadum application. Welding current then flows through the material being welded.

At the same time, network FN is timing out. When this network has timed out, thyratron FT is rendered conducting, and current is supplied through the primary P12 to render thyratrons 2TSV and 1TSV conducting in succession. Current is then supplied through the solenoid SVF and the valve FV is opened to apply forge pressure to the work M. The current flow to solenoid SVF is initiated at an instant precisely corresponding to the setting of the switches ISW and 2SW because both the anode potential for thyratron FT and the anode potentials for thyratrons 2TSV and lTSV are supplied in synchronism with the potential corresponding to this setting. Thus, the instant of operation of the valve VF may be set precisely by setting the switches 18W and 25W.

Network AN4 which determines when thyratron WT conducts, is capable of timing out in an interval of the order of one period of the supply. Thyratron WT thus conducts one period after thyratron ATS is for the first time rendered non-conducting. Thus, thyratron WT conducts approximately one and one-half periods after thyratron AT 4 conducts. Since the conduction of thyratron AT 4 starts the timing out of network FN, network FN starts to time out about one period and a half before thyratron WT conducts. Thus, network FN can be set to time out completely or to time out to any extent desirable before thyratron WT conducts. This feature is of importance because the timing out of network FN determines the instant when the forge pressure is applied and the conduction of thyratron WT causes the welding current to flow. The timed relationship between the operations of the thyratron AT4 and WT thus permits the forge pressure to be applied at any time before or during the interval during which welding current is flowing.

The welding operation now continues with the forge pressure applied so long as thyratron AT4 conducts. During this operation, the Post-Heat Unit times out and post-heat current is supplied.

When thyratron AT4 was rendered conducting, the charging of weld network WN was interrupted and the weld network began to time out. At an instant determined oy its setting, the weld network does time out and permits the hold thyratron HT to conduct. Network ANS is then charged, rendering the weld thyratron WT non-conducting and stopping the flow of welding current. But thyratron AT4 continues to conduct, maintaining thyratron ATZG non-conducting, thyratron FT conducting and thyratrons lTSV and 2TSV conducting so that valve VF remains open and the pressure remains applied to the work. The work is now permitted to solidify under the pressure.

The charging of the network ANS in addition to causing thyratron WT to stop conducting also renders thyratron ATo non-conducting. The charging of the hold network HN is then stopped, and the hold network times out. At the end of the interval of the hold network, the off thyratron OT is rendered conducting, charging the off network ON. Thyratron ST, the squeeze thyratron, is now rendered non-conducting, and the relay SR1 is denergized. Contact 615 in the circuit of thyratron FT and contact 19 are now opened, deenergizing the supply circuits to solenoids SV and SVF, and valves VP and VI are opened, permitting the movable electrode E1 to be retracted from the work. With the reduction in pressure, switch PS is also opened.

While this is taking place during the otf interval, the Sequence Timer is reset-ting itself. When the off network N is charged, the thyratron AT2 is rendered non-conducting. The network AN2 is then discharged, and the thyratron AT3 becomes conducting. The squeeze network SN is then charged and reset for a new operation. Thyratron AT4 is then rendered non-conducting, even while pressure switch PS remains closed. Network ANS is then discharged, permitting thyratron ATS to conduct to reset network AN4 and the weld network WN, both being charged. Thyratron HT is then rendered non-conducting, permitting network ANS to discharge. Thyratron ATo then becomes conducting, resetting network Thyratron OT is then rendered non-conducting, permitting network ON to discharge and be reset for a second operation.

In addition, the Forge Control Unit is reset. When thyratron AT4 becomes non-conducting, the network ANN is discharged, permitting thydratron AT20 to conduct to charge network FN and reset it. A bias is then applied to thyratron FT so that it may be rendered conducting under the control of network FN.

The welding operation is now completed. If it is desired to produce another weld, the work M is properly reset on the electrode E2, and the switch FS is again closed or remains closed and the above-described operation is repeated.

Conclusion It is seen that we have provided welding apparatus, including facilities for applying forge pressure precisely and reliably at any time during the interval during which the Welding current is flowing. This forge pressure is applied by means of a low-cost alternating current solenoid and the instant of operation of the solenoid is precisely adjusted.

Our invention has been illustrated as applied to a welder of the type disclosed in the Stadum application. It is equally as well applicable to welders of other types, either single-phase commercial frequency or polyphase or single-phase low frequency.

While we have shown and described a certain specific embodiment of our invention, many modifications there of are possible. Our invention therefore is not to be restricted except insofar as is necessitated by the spirit of the prior art.

We claim as our invention:

1. Welding apparatus including a welder having means for applying forge pressure to work, said forge pressure applying means including a first timing circuit for determining, when it times out, the instant when said forge pressure is applied; means for supplying welding current to said welder to weld said work; and a sequence timer for timing the operational steps of said welder and including a second timing circuit connected to said supply means for initiating and maintaining the supply of said current to said welder for a predetermined time interval, and means for impressing a signal to initiate the timing of said second circuit, said signal being impressed a predetermined time interval before the flow of welding current is initiated by said second circuit; said welding apparatus being characterized by connections between said signal impressing means and said first timing circuit for impressing said signal also to initiate the timing of said first timing circuit.

2. Welding apparatus including a welder having means for applying forge pressure to work to be welded; means connected to said welder for supplying welding current thereto to weld said work; a sequence timer connected to said welder for timing the operational steps of said welder during a welding cycle in welding said work, said timer including a timing circuit connected to said supply means for actuating said supply means to supply said welding current for a predetermined time interval, said circuit including a first electric discharge device which is maintained conducting during said interval, said timer also including a second electric discharge device, means for rendering said second device conducting at 11 a predetermined instant during said welding cycle, and connections between said second device and said first 'devicefor rendering said first device conducting a pre determined time interval after said second device hecomes conducting; said welding apparatus being characterized by connections between said second device and said forge pressure applying means for actuating said applying means a predetermined time interval after said second device is rendered conducting.

3. Welding'apparatus including a welder having means for applying forge pressure to Work; means for supplying alternating welding current to weld said work and a sequence timer including means connected to said current supply means for actuating said current supply means to supply current to said work during a predetermined number of periods of said alternating current and means uctuable in timed relationship with said means connected to said current supply means for causing forge pressure to be applied to said workysaid welding apparatus being characterized by forge pressure applying means having a valve actuable by a solenoid energizable by said alternating current; and by means responsive to said'forge pressure causing means, for supplying current to said solenoid, said responsive means including means'for initiating the supply of current to said solenoid at a predetermined instant in the half periods of said alternating current.

4. Welding apparatus according to claim 3 adapted to be supplied with polyphase alternating current derivable from, a plurality of supply conductors corresponding in number to the phase of said polyphas'e characterized by the fact that the sequence timer is supplied from a pair of said conductors and the means connected to the welding current supply means and the forge pressure causing means are actuable in synchronism with the potential derivable from said pair of conductors and by the further fact that the current supply means for the solenoid is supplied from, and in synchronism with, any two of said supply conductors selectable at the will of an operator.

5. Welding apparatus according to claim 4 characterized by, solenoid current supply means including a pair of electric discharge paths each defined by an anode and a cathode, and by means for conecting said paths in antiparallel between the solenoid and the selected two of the supply conductors.

6. Welding apparatus according to claim 3 characterizedby the ,factthat the responsive means includes time delay means for delaying the initiation of the supply of current to the solenoid by at least a predetermined time interval.

7. 'Welding apparatus according to claim 6 characterized by the fact that the time delay means includes means for delaying the initiation of the supply of current to the solenoid by a time interval of several half periods of the alternating current selectable at the will of an operator.

8. Resistance welding apparatus including a forge solenoid; a forge control unit having at least one electric discharge device including an anode, a cathode and a control electrode, a circuit connected between said control electrode and cathode, which circuit when actuated conditions said device to become conducting and means for connecting said anode and said cathode to said solemold for actuating said solenoid when said device conducts; a sequence timer having a squeeze electric discharge device and an auxiliary electric discharge device, each having an anode and a cathode, and means connected between said anode and cathode of said squeeze device and said auxiliary device for controlling the conductivity of said auxiliary device in accordance with the conductivity of said squeeze device; and means coupled between said anode and cathode of said auxiliary device and said control electrode and cathode of said one device for rendering said one device, when conditioned by said" circuit, conducting a predetermined time interval after said auxiliary device is conducting; the said apparatus being characterized by means connected to said circuit and responsive to said squeeze device for conditioning said one'device to become conducting only while said squeeze device is conducting.

9. Resistance welding apparatus including a forge solenoid; a forge control unit having at least one electric discharge device including an anode, a cathode and a control electrode, a circuit conected between said control electrode and cathode, which circuit when actuated conditions said device to become conducting and means for connecting said anode and said cathode to said solenoid for actuating said solenoid when said device conducts, and a sequence timer having a squeeze electric discharge device, a weld electric discharge device and an auxiliary electric discharge device, each having an anode and a cathode, and means connected between said anode and cathode of said squeeze device and said auxiliary device for controlling the conductivity of said auxiliary device in accordance with the conductivity of said. squeeze device, means coupled between said anode and oathodeof said auxiliary device and said weld device for rendering said weld device conducting a predetermined time interval after said auxiliary device becomes conducting, and means coupled between said anode and cathode of said auxiliary device and said control electrode and cathode of said one device for rendering said one device, when conditioned by said circuit, conducting another predetermined time interval after said auxiliary device is conducting; the said apparatus being characterized by means connected to said circuit and responsiveto said squeeze device for conditioning said one device to become conducting only while said squeeze device is conducting.

References Cited the file of this patent UNITED STATES PATENTS 2,118,427 Bush May 24, 1938 2,250,202 Matusia July 22, 1941 2,254,121 Mekelburg Aug. 26, 1941 2,340,085 Slepian et al. Jan. 25, 1944 2,361,229 Monteith Oct. 24, 1944 2,411,708 Bivens Nov. 26, 1946 2,452,070 Runckle Oct. 26, 1948 2,542,845 Taliaferro Feb. 20, 1951 2,590,582 Stadum et a1. Mar. 25, 1952 2,597,959 Smith May 27, 1952 

